Capitalism inevitably devolves into crony capitalism/corporatism. Indeed, what is happening in the UK is literally after decades of of increasing liberalization! So "works without fail" seems to be an exaggeration at least.
Communism and socialism don't lead to cronyism and corruption?
To the extent that the government regulates/controls commerce, you will have corruption and cronyism. Restore freedom and remove the government from commerce, and cronyism goes away. I'm guessing the UK government is HIGHLY involved in all aspects of commerce.
Remove governance and corporations will flood in to fill the void. Personally I'd rather have a master I can vote out rather than a bunch of corporations dictating how I live.